[1] Specific Aims: Langerhans cells (LC) are a specific subset of antigen presenting cells that reside in epidermis and that are highly efficient at incorporating, processing,a nd assembling various forms of antigens. Importantly, each of these events takes place within the vacuolar systems and in a manner dependent on energy generated by vacuolar ATPases (v- ATPases). We have cloned recently a full-length cDNA, 3C5, that encodes a novel subunit (termed subunit G) of murine v-ATPase. Importantly, 3C5 mRNA expression appears to be restricted to cells of dendritic cell (DC) lineage, including LC. Our working hypothesis is, therefore, that the subunit G serves as an essential and functional component of the DC- associated vacuolar systems. Specific aims are: Aim 1: To characterize subunit G protein. Aim 2: To determine the functional properties of subunit G. Aim 3: To clone the gene that encodes human subunit G.